You were born with a very powerful quirk, in fact, and the minute the heroes found out about this, you were taken from your home and taken to UA and given a Uniform, to tell the truth, you never wanted to be there and liked your life back, but you complied

All Might: "Here's your uniform, oh and also, here's your classes!"

Aizawa: "don't you think we're going a bit fast, and actually tell her what we're doing."

Nezu: "the faster the better! The class you'll be joining is out for training right now."